Write data switching for magnetic disk drives

ABSTRACT

One embodiment of the invention includes a system for writing data onto a magnetic disk. An output driver provides a first write current through a first output transistor in a first state and provides a second write current through a second output transistor in a second state. The first and second write currents can be provided to a disk write head to store opposing binary values, respectively. A bias current generator switches a first bias current between an intermediate voltage node in the second state and the first control node in the first state, and switches a second bias current between the intermediate voltage node in the first state and the second control node in the second state. The first and second bias currents can be provided to set a bias voltage at the first and second control nodes to bias the first and second output transistors, respectively.

RELATED APPLICATIONS

The present invention claims priority from U.S. Provisional Patent Application No. 60/913,165, filed Apr. 20, 2007, entitled: “Write Data Switching for Hard Disk Drives”.

TECHNICAL FIELD

This invention relates to electronic circuits, and more specifically to write data switching for magnetic disk drives.

BACKGROUND

Most personal computers and computer servers use magnetic disk drive memory storage, such as a hard disk drive. Magnetic disk drives store data based on applying a magnetic field to portions of the disk drive surface to set a magnetic polarity of the portions. The magnetic polarity thus corresponds to the binary data that is stored thereon. The magnetic field is applied based on providing a current through an inductive load that is located in the write head of the disk drive. Current that is provided in one direction through the inductive load provides a magnetic field of a first polarity that can correspond to a binary “1”, while current that is provided in the opposite direction through the inductive load provides a magnetic field of a second polarity that can correspond to a binary “0”.

SUMMARY

One embodiment of the invention includes a system for writing data onto a magnetic disk. An output driver provides a first write current through a first output transistor in a first state and provides a second write current through a second output transistor in a second state. The first and second write currents can be provided to a disk write head to store opposing binary values, respectively. A bias current generator switches a first bias current between an intermediate voltage node in the second state and the first control node in the first state, and switches a second bias current between the intermediate voltage node in the first state and the second control node in the second state. The first and second bias currents can be provided to set a bias voltage at the first and second control nodes to bias the first and second output transistors, respectively.

Another embodiment of the invention includes a method for writing data onto a magnetic disk. The method comprises activating a first switch in response to a first state of a pulse signal and conducting a current through the first switch at a magnitude that is a sum of a bias current generated from a bias current source and an overshoot current generated from an overshoot current source. The method also comprises setting a magnitude of a bias voltage at a control node to activate an output transistor associated with the control node to generate a write current at a first magnitude. The method further comprises setting a magnitude of a bias voltage at a control node to activate an output transistor to generate a write current at a first magnitude, and deactivating a second switch in response to a first state of an overshoot pulse signal to decouple the overshoot current source from the first switch. The magnitude of the current can be reduced to the magnitude of the bias current, such that the magnitude of the bias voltage changes to generate the write current at a second magnitude that is less than the first magnitude in response to deactivating the second switch.

Another embodiment of the invention includes a magnetic disk write predriver. The predriver comprises means for generating a first bias current and means for generating a first overshoot current. The predriver also comprises means for conducting a first current having a magnitude that is a sum of the first bias current and the first overshoot current to set a first bias voltage at a first control node upon a transition from a first state to a second state. The first control node can be coupled to an output transistor that is activated by the first bias voltage to control a magnitude of a write current through the output transistor. The first and second states correspond to opposing binary write values, respectively. The predriver further comprises means for deactivating the first overshoot current during the second state to set the magnitude of the first current to be approximately equal to the first bias current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a magnetic disk write system in accordance with an aspect of the invention.

FIG. 2 illustrates an example of a magnetic disk write driver system in accordance with an aspect of the invention.

FIG. 3 illustrates an example of a disk write predriver in accordance with an aspect of the invention.

FIG. 4 illustrates an example of a timing diagram associated with a magnetic disk write driver system in accordance with an aspect of the invention.

FIG. 5 illustrates an example of a method for writing data on a magnetic disk in accordance with an aspect of the invention.

DETAILED DESCRIPTION

This invention relates to electronic circuits, and more specifically to write data switching for magnetic disk drives. A disk write predriver includes a bias current generator and an overshoot current generator. The bias current generator includes transistors that are coupled to each of two control nodes, with each of the two control nodes being respectively coupled to each of two output transistors in an output driver. The bias current generator receives a pulse signal that controls a set of the transistors to switch a current source between one of the control nodes and an intermediate voltage node in response to opposing binary states of the pulse signal. The current provided by the current source sets a bias voltage at the one control node to activate the respective output transistor in the output driver to generate an output current that becomes the write current through a write head to write data onto a magnetic disk. Thus, the bias voltage is set for each of the control nodes at opposite binary states of the pulse signal to activate the respective output transistor for the generation of the write current in each respective current flow direction through the write head.

The overshoot current generator is coupled to the bias current generator. The overshoot current generator includes transistors that are coupled to each transistor in the bias current generator that is coupled to the respective one of the control nodes. The bias current generator receives an overshoot pulse signal that is a delayed version of the pulse signal. The overshoot pulse signal controls a set of the transistors to switch an overshoot current source between the respective one of the transistors in the bias current generator and the intermediate voltage node in response to opposing binary states of the overshoot pulse signal. The current provided by the overshoot current source contributes to the bias voltage at the one control node to increase the output current through the output transistor, thus increasing the write current during an overshoot phase that is defined by the amount of delay between the pulse signal and the overshoot pulse signal. Thus, upon expiration of the overshoot phase, the overshoot current generator switches the overshoot current source to the intermediate voltage node.

FIG. 1 illustrates an example of a magnetic disk write system 10 in accordance with an aspect of the invention. The system 10 includes a pulse generator 12 that receives a signal DATA as an input. The signal DATA can be, for example, a stream of data that is to be written to the magnetic disk (not shown). The pulse generator 12 generates a plurality of signals to control a write operation of the signal DATA onto the magnetic disk and provides the signals to a first disk write predriver 14 and a second disk write predriver 16. The first and second disk write predrivers 14 and 16 are configured to generate bias signals corresponding to the signal DATA and provide the bias signals to a first output driver 18 and a second output driver 20, respectively.

The first and second output drivers 18 and 20 generate output currents I_(OUT) _(—) _(X) and I_(OUT) _(—) _(Y) through the write head 22 from a positive rail voltage V_(CC) to a negative rail voltage V_(EE). Specifically, the first output driver 18 can source the output current I_(OUT) _(—) _(X) from the positive rail voltage V_(CC) and the second output driver 20 can sink the output current I_(OUT) _(—) _(X) to the negative rail voltage V_(EE), such that the output current I_(OUT) _(—) _(X) flows through the write head 22 as a write current I_(WRITE), as demonstrated in the example of FIG. 1. The write current I_(WRITE) thus generates a magnetic field through the inductive load in the write head 22 corresponding to a first binary state of data that is written to the magnetic disk. Alternatively, the first output driver 18 can source the output current I_(OUT) _(—) _(Y) from the positive rail voltage V_(CC) and the second output driver 20 can sink the output current I_(OUT) _(—) _(Y) to the negative rail voltage V_(EE), such that the output current I_(OUT) _(—) _(Y) flows through the write head 22 as the write current I_(WRITE) in the opposite direction. Therefore, the write current I_(WRITE) generates a magnetic field through the inductive load in the write head 22 in the opposite direction corresponding to the opposite binary state of data that is written to the magnetic disk.

As an example, the first and second disk write predrivers 14 and 16 can each include a bias current generator and an overshoot current generator. The bias current generator of each of the first and second disk write predrivers 14 and 16 includes switches that are coupled to each of two control nodes that correspond, respectively, to output transistors in the respective output drivers 18 and 20 that control activation of the output currents I_(OUT) _(—) _(X) and I_(OUT) _(—) _(Y). As an example, the switches in the first and second disk write predrivers 14 and 16 can actively control the output transistors in the respective output drivers 18 and 20, such that the switches in the first and second disk write predrivers 14 and 16 are activated to source or sink current, respectively, to control nodes that bias the output transistors in the respective output drivers 18 and 20. The switches in the first and second disk write predrivers 14 and 16 can be controlled based on a pulse signal that is generated from the pulse generator 12.

The overshoot current generator in the first and second disk write predrivers 14 and 16 can be configured to add an overshoot current to the bias currents that flow through the switches in the bias current generators during an overshoot phase. Specifically, because the write current I_(WRITE) is provided through an inductive load, the absolute magnitude of the write current I_(WRITE) is increased upon switching logic-states of the data that is written to the magnetic disk (i.e., direction of the flow of the write current I_(WRITE)) to overcome the inductance of the of the inductive load. The addition of the overshoot current through the switches in the bias current generator that provide the bias current can thus reduce parasitic capacitance associated with the control nodes to provide for more rapid switching. In addition, the overshoot transistors can be controlled based on an overshoot pulse signal that is a time-delayed version of the pulse signal that controls the switches in the bias current generator. As a result, the overshoot current does not need to be time-aligned with the beginning of a logic-state transition of the pulse signal that controls the switches in the bias current generator, as the overshoot phase can merely be defined as the time delay difference pulse signal and the overshoot pulse signal.

FIG. 2 illustrates an example of a magnetic disk write driver system 100 in accordance with an aspect of the invention. The system 100 includes a disk write predriver 102 and an output driver 104. As an example, the disk write predriver 102 and the output driver 104 can correspond to the first disk write predriver 14 and the first output driver 18, respectively. Therefore, reference is to be made to the example of FIG. 1 in the following discussion of the example of FIG. 2.

The disk write predriver 102 receives a control voltage V_(DC2) that sets a first bias voltage V_(BIAS) _(—) _(X) across a resistor R_(X) at a first control node 106 and a second bias voltage V_(BIAS) _(—) _(Y) across a resistor R_(Y) at a second control node 108. The control voltage V_(DC2) can have a magnitude, for example, that is sufficient to keep a first output transistor Q₁ and a second output transistor Q₂ that are included in the output driver 104 deactivated, as described in greater detail below. As also demonstrated below, the relative magnitude of the first and second bias voltages V_(BIAS) _(—) _(X) and V_(BIAS) _(—) _(Y) are determinative of a direction of the write current I_(WRITE) through the write head 22, and thus the binary logic state of the write data based on the polarity of the associated magnetic field.

The disk write predriver 102 includes a bias current generator 110. The bias current generator 110 is configured to receive a pulse signal PLS, such as generated from the pulse generator 12 in the example of FIG. 1. Thus, the pulse signal PLS can be a binary signal that corresponds to the write data that is to be stored on the magnetic disk. The bias current generator 110 is thus configured to generate a first bias current and a second bias current in response to the binary state of the pulse signal PLS. In the example of FIG. 2, the bias currents are demonstrated as a first current I_(CTRL) _(—) _(X) and a second current I_(CTRL) _(—) _(Y). As an example, the first and second currents I_(CTRL) _(—) _(X) and I_(CTRL) _(—) _(Y) can be provided through transistors, such as being activated by opposing binary states of the pulse signal PLS. As such, the first and second currents I_(CTRL) _(—) _(X) and I_(CTRL) _(—) _(Y) can have a magnitude that is sufficient to adjust the respective magnitudes of the bias voltages V_(BIAS) _(—) _(X) and V_(BIAS) _(—) _(Y), such as to decrease the respective one of the bias voltages V_(BIAS) _(—) _(X) and V_(BIAS) _(—) _(Y) by a magnitude sufficient to activate respective output transistors (e.g., approximately 300 mV). As an example, the bias current generator 110 can generate the first and second currents I_(CTRL) _(—) _(X) and I_(CTRL) _(—) _(Y) mutually exclusively, such that the bias current generator 110 can provide the first current I_(CTRL) _(—) _(X) to decrease the first bias voltage V_(BIAS) _(—) _(X) or can provide the second current I_(CTRL) _(—) _(Y) to decrease the second bias voltage V_(BIAS) _(—) _(Y).

The output driver 104 includes a first driver 112 and a second driver 114. The first driver 112 interconnects the first control node 106 and a base of a first switch Q₁, demonstrated in the example of FIG. 2 as a PNP-type bipolar junction transistor (BJT). Similarly, the second driver 114 interconnects the second control node 108 and a base of a second switch Q₂. The first and second drivers 112 and 114 are configured to set the appropriate bias levels for switching the first and second switches Q₁ and Q₂, such as in a linear mode of operation, based on the respective first and second bias voltages V_(BIAS) _(—) _(X) and V_(BIAS) _(—) _(Y).

In response to the bias current generator 110 providing the first current I_(CTRL) _(—) _(X), the first bias voltage V_(BIAS) _(—) _(X) is decreased. Thus, the first switch Q₁ is activated based on a logic-low state output from the first driver 112 to generate the first output current I_(OUT) _(—) _(X) via the positive rail voltage V_(CC) and a resistor R_(OUT) to provide the write current I_(WRITE) in a first direction through the write head 22. Likewise, in response to the bias current generator 110 generating the second current I_(CTRL) _(—) _(Y), the second bias voltage V_(BIAS) _(—) _(Y) is decreased. Thus, the second switch Q₂ is activated based on a logic-low state output from the second driver 114 to generate the second output current I_(OUT) _(—) _(Y) to provide the write current I_(WRITE) in the opposite direction through the write head 22. Accordingly, the bias current generator 110 provides the first current I_(CTRL) _(—) _(X) to decrease the first bias voltage V_(BIAS) _(—) _(X) to activate the first switch Q₁ and provides the second current I_(CTRL) _(—) _(Y) to decrease the second bias voltage V_(BIAS) _(—) _(Y) to activate the second switch Q₂.

As described above in the example of FIG. 1, the write head 22 includes an inductive load. As a result, the write head 22 can be slow to react to changes in the write current I_(WRITE) in generating the magnetic field to write data onto the magnetic disk based on the low pass filter characteristic of inductive loads. Therefore, the disk write predriver 102 also includes an overshoot current generator 116 configured to generate a first overshoot current I_(OS) _(—) _(X) and a second overshoot current I_(OS) _(—) _(Y). The first and second overshoot currents I_(OS) _(—) _(X) and I_(OS) _(—) _(Y) are generated, respectively, based on opposite states of an overshoot pulse signal PLS_(OS). As an example, the overshoot pulse signal PLS_(OS) can be a delayed version of the pulse signal PLS, such as generated by the pulse generator 12 in the example of FIG. 1. Thus, an overshoot phase can be defined based on the amount of delay between the pulse signal PLS and the overshoot pulse signal PLS_(OS).

In the example of FIG. 2, the bias current generator 110 interconnects the overshoot current generator 116 and the first and second control nodes 106 and 108. Therefore, during an overshoot phase, the first and second overshoot currents I_(OS) _(—) _(X) and I_(OS) _(—) _(Y) can flow through transistors in both the overshoot current generator 116, such as based on being activated by the respective opposite binary states of the overshoot pulse signal PLS_(OS), and through the transistors in the bias current generator 110. Accordingly, during an overshoot phase, the first current I_(CTRL) _(—) _(X) or the second current I_(CTRL) _(—) _(Y) can have a magnitude that includes both a bias current, as generated by the bias current generator 110, and the respective overshoot current I_(OS) _(—) _(X) or I_(OS) _(—) _(Y). The addition of the first and second overshoot currents I_(OS) _(—) _(X) and I_(OS) _(—) _(Y) to the bias currents in the respective currents I_(CTRL) _(—) _(X) and I_(CTRL) _(—) _(Y) can thus operate to increase the magnitude of the respective output currents I_(OUT) _(—) _(X) and I_(OUT) _(—) _(Y) during an overshoot phase, such as at a binary state transition of the pulse signal PLS.

Based on the magnitude of the control voltage V_(DC2) being sufficient to hold the first and second switches Q₁ and Q₂ in a deactivated state, the example of FIG. 2 demonstrates that the currents I_(CTRL) _(—) _(X) and I_(CTRL) _(—) _(Y) are generated, respectively, to activate the switches Q₁ and Q₂ by decreasing the magnitudes of the respective first and second bias voltages V_(BIAS) _(—) _(X) and V_(BIAS) _(—) _(Y). Therefore, the magnetic disk write driver system 100 exhibits active switching in generating the write current I_(WRITE) by activating the first and second currents I_(CTRL) _(—) _(X) and I_(CTRL) _(—) _(Y) to activate the respective first and second switches Q₁ and Q₂ as opposed to passive switching, such as by deactivating the first and second currents I_(BIAS) _(—) _(X) and I_(BIAS) _(—) _(Y) to activate the respective second and first switches Q₂ and Q₁. As a result, the magnetic disk write driver system 100 does not experience transistor deactivation delays to delay activation of the switches Q₁ and Q₂, such as could result from passive switching of the first and second switches Q₁ and Q₂.

In addition, as described above, the first and second currents I_(CTRL) _(—) _(X) and I_(CTRL) _(—) _(Y) can be composite currents during an overshoot phase that includes both a bias current and an overshoot current. As such, the first and second currents I_(CTRL) _(—) _(X) and I_(CTRL) _(—) _(Y) can each be generated to flow through a single transistor. Therefore, parasitic capacitance associated with the first and second control nodes 106 and 108 can be mitigated, such that the first and second bias voltages V_(BIAS) _(—) _(X) and V_(BIAS) _(—) _(Y) can adjust magnitudes more quickly. As a result, the first and second switches Q₁ and Q₂ can experience faster switching times.

Furthermore, timing problems associated with the switching of the first and second overshoot currents I_(OS) _(—) _(X) and I_(OS) _(—) _(Y) can be mitigated. Specifically, an overshoot phase could be substantially short (e.g., 100 picoseconds), such that it could be shorter than a width of a write data bit to minimize slew of the write current I_(WRITE) from one polarity to another at a write data binary state transition. Individual control of the first and second overshoot currents I_(OS) _(—) _(X) and I_(OS) _(—) _(Y), such as in response to individual overshoot signal pulses that could define the overshoot phase at each polarity transition of the write current I_(WRITE), could result in timing problems in propagating individual overshoot pulse signals through the system 10 to align the individual overshoot pulse signals with respective transitions of the pulse signal PLS. However, based on the overshoot pulse signal PLS_(OS) being a single signal that is a time delayed version of the pulse signal PLS, timing problems in generating the first and second overshoot currents I_(OS) _(—) _(X) and I_(OS) _(—) _(Y) can be substantially mitigated.

FIG. 3 illustrates an example of the disk write predriver 102 in accordance with an aspect of the invention. As demonstrated in the example of FIG. 3, the disk write predriver 102 includes the bias current generator 110 and the overshoot current generator 116. The bias current generator 110 includes two pairs of switches, a switch Q₃ and a switch Q₄ as well as a switch Q₅ and a switch Q₆. The switches Q₃ through Q₆ are all demonstrated in the example of FIG. 3 as NPN BJTs, but can instead implement PNP BJTs or field effect transistors (FETs). However, it is to be understood that the bias current generator 110 is not limited to the use of NPN BJTs. The switch Q₃ interconnects the first control node 106 at a collector and a first bias current source 120 at an emitter. Similarly, the switch Q₅ interconnects the second control node 108 at a collector and a second bias current source 122 at an emitter. As demonstrated in the example of FIG. 3, the first and second bias current sources 120 and 122 generate a current having a magnitude of I_(BIAS) to a negative voltage rail V_(EE), which could be negative relative to ground. The switches Q₄ and Q₆ interconnect a common mode control node, demonstrated in the example of FIG. 3 as ground, and the respective first and second bias current sources 120 and 122. The switches Q₃ and Q₆ have bases that are coupled directly to the pulse signal PLS, while the switches Q₄ and Q₅ have bases that are coupled to the pulse signal PLS via a signal polarity inverter 126 configured to provide a signal that is a substantially opposite polarity signal as the pulse signal PLS. It is to be understood that, although the pulse signal PLS is demonstrated and discussed as appearing digital, it can be an analog signal.

The overshoot current generator 116 includes two pairs of switches, a switch Q₇ and a switch Q₈ as well as a switch Q₉ and a switch Q₁₀. Similar to the bias current generator 110, the switches Q₇ through Q₁₀ are all demonstrated in the example of FIG. 3 as NPN BJTs. The switch Q₇ interconnects the emitter of the switch Q₃ at a collector and a first overshoot current source 128 at an emitter. Similarly, the switch Q₁₀ interconnects the emitter of the switch Q₅ at a collector and a second overshoot current source 130 at an emitter. As demonstrated in the example of FIG. 3, the first and second overshoot current sources 128 and 130 generate a current having a magnitude of I_(OS) to the negative voltage rail V_(EE). The switches Q₈ and Q₁₀ interconnect ground and the respective first and second overshoot current sources 128 and 130. The switches Q₈ and Q₉ have bases that are coupled directly to the overshoot pulse signal PLS_(OS), while the switches Q₇ and Q₁₀ have bases that are coupled to the overshoot pulse signal PLS_(OS) via a signal polarity inverter 132 configured to provide a signal that is a substantially opposite polarity signal as the overshoot pulse signal PLS_(OS). It is to be understood that, although the overshoot pulse signal PLS_(OS) is demonstrated and discussed as appearing digital, it can be an analog signal.

FIG. 4 illustrates an example of a timing diagram 150 associated with the magnetic disk write driver system 100. It is to be understood that the timing diagram 150 is demonstrated in the example of FIG. 4 as an ideal timing diagram, such that inherent signal delays and minor magnitude variations are not illustrated. At a time T₀, the pulse signal PLS switches from a logic-low (i.e., binary “0”) state to a logic-high (i.e., binary “1”) state. In response, the switches Q₄ and Q₅ are deactivated and the switches Q₃ and Q₆ are activated. Therefore, the switch Q₃ couples the first control node 106 to the first bias current source 120 and the switch Q₆ couples the second bias current source 122 to ground.

In addition, at a time prior to the time T₀, the overshoot pulse signal PLS_(OS) is switched logic-low, and thus remains logic-low at the time T₀. Therefore, the switches Q₈ and Q₉ have been deactivated and the switches Q₇ and Q₁₀ have been activated. Thus, just prior to the time T₀, the switch Q₄ and the switch Q₇ were each activated, such that the switch Q₄ conducted a composite current from ground having a magnitude that is a sum of I_(OS) (i.e., the first overshoot current I_(OS) _(—) _(X)) and I_(BIAS), and the switch Q₇ conducted the current I_(OS) _(—) _(X) having a magnitude of I_(OS). However, at the time T₀, upon deactivation of the switch Q₄ and activation of the switch Q₃, the switch Q₃ now conducts the composite current I_(CTRL) _(—) _(X), having the magnitude that is the sum of I_(BIAS) and I_(OS), from the first control node 106. The switch Q₇ continues to conduct the current I_(OS) _(—) _(X) at the time T₀. Also at the time T₀, the switch Q₆ conducts a composite current from ground having a magnitude that is a sum of I_(OS) (i.e., the second overshoot current I_(OS) _(—) _(Y)) and I_(BIAS), and the switch Q₉ conducts the second overshoot current I_(OS) _(—) _(Y) having a magnitude of I_(OS).

In response to the first current I_(CTRL) _(—) _(X), the first bias voltage V_(BIAS) _(—) _(X) decreases to activate the first switch Q₁, resulting in the generation of the output current I_(OUT) _(—) _(X). Due to the inclusion of the first overshoot current I_(OS) _(—) _(X) in the first current I_(CTRL) _(—) _(X), the time T₀ marks the beginning of an overshoot phase based on the binary state transition of the pulse signal PLS. Thus, the write current I_(WRITE) is demonstrated at the time T₀ as having a positive overshoot magnitude of I₁, such that the write head 22 writes a binary “1” to the magnetic disk. It is to be understood that the write current I_(WRITE) has a positive value, relative to 0 amps as demonstrated in the timing diagram 150, based on the direction of the write current I_(WRITE) through the write head 22 as demonstrated in the example of FIG. 1.

As described above, the overshoot pulse signal PLS_(OS) can be configured as a delayed version of the pulse signal PLS. At a time T₁, the overshoot pulse signal PLS_(OS) is asserted, thus ending the overshoot phase. Accordingly, in the example of FIG. 4, the overshoot phase has a duration that is defined by the amount of delay between the pulse signal PLS and the overshoot pulse signal PLS_(OS) (i.e., from T₀ T₁). In response to the assertion of the overshoot pulse signal PLS_(OS) at the time T₁, the switches Q₇ and Q₁₀ are deactivated and the switches Q₈ and Q₉ are activated. Therefore, the first overshoot current I_(OS) _(—) _(X) no longer flows through the switch Q₃. As a result, the current I_(CTRL) _(—) _(X) is reduced to a magnitude of I_(BIAS) based on the switch Q₃ only conducting the current that is generated from the first bias current source 120. Accordingly, the first bias voltage V_(BIAS) _(—) _(X) increases, resulting in a decrease of the magnitude of the output current I_(OUT) _(—) _(X), and thus a decrease of the write current I_(WRITE) to a magnitude of I₂.

Also at the time T₁, because the switch Q₈ is activated, the overshoot current I_(OS) generated from the first overshoot current source 128 flows from ground to the negative rail voltage V_(EE) through the switch Q₈. In addition, because the switch Q₈ is activated, the switch Q₉ conducts the second overshoot current I_(OS) _(—) _(Y) with an approximate magnitude of I_(OS) as generated by the second overshoot current source 130. The switch Q₆, which was activated at the time T₀, now conducts a composite current from ground having a magnitude that is a sum of the bias current I_(BIAS) generated from the second bias current source 122 and the second overshoot current I_(OS) _(—) _(Y).

At a time T₂, the pulse signal PLS is deasserted, thus switching from a logic-high state to a logic-low state. As demonstrated in the example of FIG. 3, the length of the assertion of the pulse signal from the time T₀ the time T₂ was sufficient for the magnetic field generated by the write current I_(WRITE) flowing through the write head 22 to write three consecutive logic “1” values to the magnetic disk. However, at the time T₂, because the pulse signal PLS is deasserted, the next bit to be written to the magnetic disk is a logic “0”.

In response to the deassertion of the pulse signal PLS, the switches Q₃ and Q₆ are deactivated and the switches Q₄ and Q₅ are activated. Therefore, the switch Q₅ couples the second control node 108 to the second bias current source 122 and the switch Q₄ couples the first bias current source 120 to ground. However, the switch Q₉ was activated at the time T₁ and remains activated at the time T₂, thus continuing to conduct the second overshoot current I_(OS) _(—) _(Y) at the time T₂. Therefore, at the time T₂, the switch Q₅ now conducts the composite current I_(CTRL) _(—) _(Y), having the magnitude that is the sum of I_(OS) (i.e., the second overshoot current I_(OS) _(—) _(Y)) and I_(BIAS), from the second control node 108. Thus, the write current I_(WRITE) is demonstrated at the time T₂ as having a negative overshoot magnitude of −I₁, such that the write head 22 writes the binary “0” to the magnetic disk. Specifically, because the write current I_(WRITE) flows through an inductive load, the overshoot magnitude −I₁ is effective to reverse the magnetic field generated by the write head 22 more rapidly for a stable transition of writing a binary “1” to a binary “0” consecutively. Also at the time T₂, the switch Q₄ conducts a composite current from ground having a magnitude that is a sum of I_(OS) (i.e., the first overshoot current I_(OS) _(—) _(X)) and I_(BIAS), and the switch Q₇ conducts the second overshoot current I_(OS) _(—) _(Y) having a magnitude of I_(OS).

At a time T₃, the overshoot pulse signal PLS_(OS) is deasserted, thus ending the overshoot phase. In response, the switches Q₈ and Q₉ are deactivated and the switches Q₇ and Q₁₀ are activated. Therefore, the second overshoot current I_(OS) _(—) _(Y) no longer flows through the switch Q₅. As a result, the current I_(CTRL) _(—) _(Y) is reduced to a magnitude of I_(BIAS) based on the switch Q₅ only conducting the current that is generated from the second bias current source 122. Accordingly, the second bias voltage V_(BIAS) _(—) _(Y) increases, resulting in a decrease of the magnitude of the output current I_(OUT) _(—) _(Y), and thus an increase (i.e., absolute magnitude decrease) of the write current I_(WRITE) to a magnitude of −I₂.

Also at the time T₃, because the switch Q₁₀ is activated, the overshoot current I_(OS) generated from the second overshoot current source 130 flows from ground to the negative rail voltage V_(EE) through the switch Q₁₀. In addition, because the switch Q₇ is activated, the switch Q₇ conducts the first overshoot current I_(OS) _(—) _(X) with an approximate magnitude of I_(OS) as generated by the first overshoot current source 128. The switch Q₄, which was activated at the time T₂, now conducts a composite current from ground having a magnitude that is a sum of the bias current I_(BIAS) generated from the first bias current source 120 and the first overshoot current I_(OS) _(—) _(X).

At a time T₄, another logic transition of the pulse signal PLS occurs from logic-low to logic-high. Accordingly, the magnetic disk write driver system 100 operates similar to as described above at the time T₀. As demonstrated in the example of FIG. 4, the duration of the logic-low pulse of the pulse signal PLS from the time T₂ to the time T₄ was sufficient for the magnetic field generated by the write current I_(WRITE) flowing through the write head 22 to write two consecutive logic “0” values to the magnetic disk. At time T₅, after two consecutive logic “1” values have been written to the magnetic disk, another logic transition of the pulse signal PLS occurs from logic-high to logic-low, thus repeating the operation as described above at the time T₂. Further single-bit transitions occur at subsequent times T₆ and T₇.

Based on the examples of FIGS. 1-4, it is demonstrated that substantially high data-rates can be achieved, such as 4 gigabits per second (i.e., 1 bit every 250 picoseconds). Such high data-rates or greater can be achieved based on, for example, active switching in generating the write current I_(WRITE) by activating the first and second currents I_(CTRL) _(—) _(X) and I_(CTRL) _(—) _(Y) to activate the respective first and second switches Q₁ and Q₂, as opposed to passive switching. As a result, the magnetic disk write driver system 100 does not experience transistor deactivation delays to delay activation of the switches Q₁ and Q₂. In addition, the substantially higher data-rates can also be achieved, for example, based on mitigating parasitic capacitance associated with each of the first and second control nodes 106 and 108, such as based on the coupling of only a single switch, Q₃ and Q₅, respectively, as demonstrated in the example of FIG. 3. Thus, the first and second switches Q₁ and Q₂ can be switched faster based on more rapid changes that can be realized in the first and second bias voltages V_(BIAS) _(—) _(X) and V_(BIAS) _(—) _(Y). Furthermore, timing problems associated with aligning the first and second overshoot currents I_(OS) _(—) _(X) and I_(OS) _(—) _(Y) with respective transitions of the pulse signal PLS, such as based on individual control of the first and second overshoot currents I_(OS) _(—) _(X) and I_(OS) _(—) _(Y), can be mitigated based on configuring the overshoot pulse signal PLS_(OS) as a single signal that is a time delayed version of the pulse signal PLS.

It is to be understood that the magnetic disk write driver system 100 is not intended to be limited to the example of FIGS. 2 and 3. Specifically, as described above, the disk write predriver 102 and the output driver 104 can be configured as the first disk write predriver 14 and the first output driver 18, respectively, in the example of FIG. 1. Therefore, a disk write predriver and an output driver that are configured substantially similar to the disk write predriver 102 and the output driver 104 can be configured as the second disk write predriver 16 and the second output driver 20, such that the substantially similar disk write predriver and output driver can be configured as substantial mirror-images of the disk write predriver 102 and the output driver 104. Specifically, the substantially similar disk write predriver can be configured with PNP BJTs, such that currents I_(CTRL) _(—) _(X) and I_(CTRL) _(—) _(Y) can be sourced to respective first and second control nodes from the positive rail voltage V_(CC). Likewise, the substantially similar output driver can be configured with NPN BJTs that sink the write current I_(WRITE) from the write head 22 to the negative voltage rail V_(EE) in response to respective increased magnitudes of the bias voltages V_(BIAS) _(—) _(X) and V_(BIAS) _(—) _(Y) on the mirror-image control nodes.

In addition, it is to be understood that the pulse signal PLS and the overshoot pulse signal PLS_(OS) need not be limited to single-ended signals, but can also be implemented as differential signals. As such, the signal polarity inverters 126 and 132 can be obviated, as the opposite signal of the respective differential pulse signal pair PLS and overshoot pulse signal pair PLS_(OS) can be implemented to control the switches Q₄ and Q₅ and switches Q₇ and Q₁₀, respectively. Also, the bias current generator 110 and the overshoot current generator 116 are not limited to the example of FIG. 3. Furthermore, the generation of the currents I_(CTRL) _(—) _(X) and I_(CTRL) _(—) _(Y) is not limited to the switching arrangements of the switches Q₃ through Q₆ and the switches Q₇ through Q₁₀. Specifically, any of a variety of configurations of switches can be implemented to generate the currents I_(CTRL) _(—) _(X) and I_(CTRL) _(—) _(Y) having a magnitude of I_(BIAS) and a magnitude of I_(BIAS) plus I_(OS) during an overshoot phase. Accordingly, the magnetic disk write driver system 100 can be implemented in any of a variety of ways.

In view of the foregoing structural and functional features described above, certain methods will be better appreciated with reference to FIG. 5. It is to be understood and appreciated that the illustrated actions, in other embodiments, may occur in different orders and/or concurrently with other actions. Moreover, not all illustrated features may be required to implement a method.

FIG. 5 illustrates an example of a method 200 for writing data on a magnetic disk in accordance with an aspect of the invention. At 202, a first switch is activated in response to a first state of a pulse signal. The pulse signal can be generated from a pulse generator and can correspond to a data stream that is to be written onto the magnetic disk. At 204, a current is conducted through the first switch at a magnitude that is a sum of a bias current generated from a bias current source and an overshoot current generated from an overshoot current source. The bias current and the overshoot current can be sourced from a positive rail voltage or can be sinked to a negative rail voltage. The inclusion of both the bias current and the overshoot current can be during an overshoot phase to quickly reverse a magnetic field generated by a write current through a write head.

At 206, a magnitude of a bias voltage is set at a control node to activate an output transistor associated with the control node to generate a write current at a first magnitude. The first magnitude can be substantially high so as to reverse the magnetic field for writing an opposite binary state bit to the magnetic disk. The output transistor can be one of two concurrently activated output transistors to conduct the current through the write head, one to source the write current and one to sink the write current. At 208, an overshoot pulse signal is generated as a substantially delayed version of the pulse signal. The amount of delay between the pulse signal and the overshoot pulse signal can define the overshoot phase.

At 210, a second switch is deactivated in response to a first state of the overshoot pulse signal to decouple the overshoot current source from the first switch. Another switch can be concurrently activated to conduct the overshoot current between the overshoot current source and an intermediate voltage node, such as ground. At 212, the magnitude of the current is reduced to the magnitude of the bias current and the magnitude of the bias voltage changes to generate the write current at a second magnitude that is less than the first magnitude in response to deactivating the second switch. The magnitude of the write current can be absolute, such that the decrease can also apply to a negative current flow through the write head for opposite binary states of the data written to the magnetic disk. The method 200 can be repeated for transitions to an opposite binary state of data that is to be written to the magnetic disk, such as based on a second state of the pulse signal.

What have been described above are examples of the invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the invention are possible. Accordingly, the invention is intended to embrace all such alterations, modifications, and variations that fall within the scope of this application, including the appended claims. 

1. A system for writing data onto a magnetic disk, the system comprising: an output driver configured to provide a first write current through a first output transistor in a first state and to provide a second write current through a second output transistor in a second state, the first and second write currents being provided to a disk write head to store opposing binary values, respectively, on the magnetic disk; and a disk write predriver comprising a bias current generator that is configured to switch a first bias current between an intermediate voltage node in the second state and a first control node in the first state and to switch a second bias current between the intermediate voltage node in the first state and a second control node in the second state, the first and second bias currents being provided to set a bias voltage at the first and second control nodes to bias the first and second output transistors, respectively.
 2. The system of claim 1, wherein the disk write predriver comprises an overshoot current generator configured to add an overshoot current to the first and second bias currents during an overshoot phase upon switching between the first and second states, the bias voltage being set based on the addition of the overshoot current to the first bias current in the first state to increase the first write current and based on the addition of the overshoot current to the second bias current in the second state to increase the second write current.
 3. The system of claim 1, wherein the bias current generator comprises a first switch that interconnects a first current source and the first control node, a second switch that interconnects the first current source and the intermediate voltage node, a third switch that interconnects a second current source and the second control node, and a fourth switch that interconnects the second current source and the intermediate voltage node, the first and second current sources being configured to generate the first and second bias currents, respectively.
 4. The system of claim 3, wherein the first and second states correspond to first and second logic-states of a pulse signal, and wherein the first and fourth switches are activated substantially concurrently based on the first state of the pulse signal and the second and third switches are activated substantially concurrently based on the second state of the pulse signal.
 5. The system of claim 4, wherein the bias current generator is interconnected between an overshoot current generator and the first and second control nodes such that, during an overshoot phase upon switching from the second state to the first state, the first switch conducts a composite current that is a sum of the first bias current and an overshoot current, and during an overshoot phase upon switching from the first state to the second state, the third switch conducts a composite current that is a sum of the second bias current and the overshoot current.
 6. The system of claim 5, wherein the overshoot current generator is controlled by an overshoot pulse signal that is a delayed version of the pulse signal, the overshoot pulse signal having a first state corresponding to the first state of the pulse signal and a second state corresponding to the second state of the pulse signal, an overshoot phase being defined by a duration of the delay between the pulse signal and the overshoot pulse signal.
 7. The system of claim 6, wherein the overshoot current generator comprises a fifth switch that interconnects a first overshoot current source and the first switch, a sixth switch that interconnects the first overshoot current source and the intermediate voltage node, a seventh switch that interconnects a second overshoot current source and the third switch, and an eighth switch that interconnects the second overshoot current source and the intermediate voltage node, the first and second overshoot current sources each being configured to generate the overshoot current.
 8. The system of claim 7, wherein the sixth and seventh switches are activated substantially concurrently based on the first state of the overshoot pulse signal and the fifth and eighth switches are activated substantially concurrently based on the second state of the overshoot pulse signal.
 9. The system of claim 1, wherein the bias current generator comprises: a first switch coupled to the first control node and configured to conduct a first composite current that is a sum of the first bias current and an overshoot current during a first overshoot phase upon a transition from the second state to the first state; and a second switch coupled to the second control node and configured to conduct a second composite current that is a sum of the second bias current and the overshoot current during a second overshoot phase upon a transition from the first state to the second state.
 10. The system of claim 9, wherein the first composite current is reduced in magnitude to the first bias current upon expiration of the first overshoot phase and the second composite current is reduced in magnitude to the second bias current upon expiration of the second overshoot phase.
 11. A method for writing data onto a magnetic disk, the method comprising: activating a first switch in response to a first state of a pulse signal; conducting a current through the first switch at a magnitude that is a sum of a bias current generated from a bias current source and an overshoot current generated from an overshoot current source; setting a magnitude of a bias voltage at a control node to activate an output transistor to generate a write current at a first magnitude; and deactivating a second switch in response to a first state of an overshoot pulse signal to decouple the overshoot current source from the first switch, the magnitude of the current being reduced to the magnitude of the bias current, such that the magnitude of the bias voltage changes to generate the write current at a second magnitude that is less than the first magnitude in response to deactivating the second switch.
 12. The method of claim 11, wherein the current is a first current, the bias voltage is a first bias voltage, the control node is a first control node, the output transistor is a first output transistor, and the write current is a first write current, the method further comprising: deactivating the first switch and activating a third switch in response to a second state of the pulse signal; conducting a second current through the third switch at a magnitude that is a sum of the bias current and the overshoot current; setting a magnitude of a second bias voltage at a second control node to activate a second output transistor to generate a second write current at the first magnitude; and deactivating a fourth switch in response to a second state of the overshoot pulse signal to decouple the overshoot current source from the third switch, the magnitude of the second current being reduced to the magnitude of the bias current, such that the magnitude of the second bias voltage changes to generate the second write current at the second magnitude in response to deactivating the fourth switch.
 13. The method of claim 11, further comprising generating the overshoot pulse signal as a delayed version of the pulse signal.
 14. The method of claim 13, further comprising setting a time duration between activating the first switch and deactivating the second switch based on an amount of delay between the pulse signal and the overshoot pulse signal.
 15. The method of claim 11, wherein the bias current source is a first bias current source, the overshoot current source is a first overshoot current source, and the control node is a first control node, the method further comprising: activating a third switch in response to the first state of an overshoot pulse signal to couple the first overshoot current source to an intermediate voltage node; and activating a fourth switch in response to the first state of an overshoot pulse signal to couple a second overshoot current source to a fifth switch, the fifth switch interconnecting a second control node and a second bias current source.
 16. The method of claim 15, wherein the current is a first current, the method further comprising: deactivating the first switch and activating a sixth switch in response to a second state of the pulse signal, the sixth switch interconnecting the first current source and the intermediate voltage node; and activating the fifth switch in response to the second state of the pulse signal to conduct a second current through the fifth switch, the second current having a magnitude that is a sum of the bias current and the overshoot current.
 17. A magnetic disk write predriver comprising: means for generating a first bias current; means for generating a first overshoot current; means for conducting a first current having a magnitude that is a sum of the first bias current and the first overshoot current to set a first bias voltage at a first control node upon a transition from a first state to a second state, the first control node being coupled to an output transistor that is activated by the first bias voltage to control a magnitude of a write current through the output transistor, the first and second states corresponding to opposing binary write values, respectively; and means for deactivating the first overshoot current during the second state to set the magnitude of the first current to be approximately equal to the first bias current.
 18. The predriver of claim 17, wherein the means for conducting is controlled by a pulse signal and the means for deactivating is controlled by an overshoot pulse signal that is a delayed version of the pulse signal.
 19. The predriver of claim 17, further comprising: means for switching the first current from an intermediate voltage node to the first control node upon the transition from the first state to the second state; and means for switching the overshoot current from the means for conducting to the intermediate voltage node upon expiration of an overshoot phase during the second state.
 20. The predriver of claim 17, further comprising: means for generating a second bias current; means for generating a second overshoot current; means for conducting a second current having a magnitude that is a sum of the second bias current and the second overshoot current to set a second bias voltage at a second control node upon a transition from the second state to the first state, the second control node being coupled to a second output transistor that is activated by the second bias voltage to control a magnitude of a second write current through the second output transistor; and means for deactivating the second overshoot current during the first state to set the magnitude of the second current to be approximately equal to the second bias current. 